:: Ord a => [a] -> [a] -package:html-entities -package:ghc -package:extra -package:incipit-base -package:integration -package:mono-traversable -package:imports -package:witherable -package:basement -package:lens -package:generic-deriving -package:statistics package:parsers
Take a parser that may consume input, and on failure, go back to where
we started and fail as if we didn't consume input.